1. Field of the Invention
The present invention relates to a method and system for processing image data in MRI (Magnetic Resonance Imaging).
2. Description of the Related Art
A magnetic resonance phenomenon is a phenomenon in which an atomic nucleus having a spin and a magnetic moment which are not zero, in a static field, resonantly absorbs/emits only an electromagnetic wave having a specific frequency. This atomic nucleus resonates at an angular frequency .omega..sub.0 (.omega..sub.0 =2.pi..nu..sub.0, .nu..sub.0 : Larmor frequency) given by the following equation: EQU .omega..sub.0 =.gamma.H.sub.0
where .gamma. is the gyromognetic ratio inherent in the type of atomic nucleus, and H.sub.0 is the static field strength.
An MRI apparatus detects an electromagnetic wave excited by the phenomenon as an MR (Magnetic Resonance) signal, and processes the MR signal, thus acquiring diagnostic data, e.g., a slice image of a subject, from information such as an atomic nucleus density, a longitudinal relaxation time T1, a transverse relaxation time T2, a flow, and a chemical shift.
Diagnostic data of all the portions of a subject placed in a static field can be acquired. In an actual apparatus, however, diagnostic data of a specific portion is acquired due to the limitations of an apparatus design or clinical requirements of an image.
In this case, a two dimensional Fourier transform method and a three dimensional Fourier transform method which are classified as phase-encoding methods are used as imaging methods. In the two dimensional Fourier method, data of a specific two dimensional surface (having a predetermined thickness) of a subject to be examined, i.e., two dimensional data (slice data) is acquired. In the three dimensional Fourier transform method, data of a specific three dimensional region of the subject, i.e., three dimensional data (volume data) is acquired. By performing image reconstruction processes on these data, a two dimensional image (slice image) and a three dimensional image (stereoscopic image) are reconstructed.
Note that an arbitrary sectional image can be acquired by an image reconstruction method and a high-speed arbitrary sectional image reconstruction method utilizing three dimensional Fourier transform with respect to the three dimensional data. In addition, a stereoscopic image viewed from a desired direction can be acquired by the image reconstruction method and a three dimensional surface display method utilizing Fourier transforms with respect to the three dimensional data.
The above-described arbitrary sectional image and stereoscopic image can be effectively used for diagnosis and simulation of a surgical operation. If, for example, a stereoscopic image acquired by volume-scanning a head as a diagnosis portion, and sagittal, coronal, and axial sectional images of arbitrary portions of the stereoscopic image are displayed, the three dimensional position and range of a lesion present in the head can be clearly recognized.
In order to acquire the above stereoscopic image or the arbitrary sectional images, however, a data acquisition time of several minutes to several tens minutes is required. Even if a special arithmetic unit is employed, it takes several minutes to perform data processing.
As described above, when an image is to be acquired by the image reconstruction method utilizing three dimensional Fourier transform, a long period of time is consumed from the start of scanning till an image display. For this reason, in an image diagnosis process, the diagnostic efficiency of the doctor is degraded.
Therefore, a strong demand has arisen for an apparatus for performing image processing and an image display of two and three dimensional data so as to clearly recognize the three dimensional position and range of a lesion.